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ADS805 offset

Len Epstein
Prodigy 40 points
Other Parts Discussed in Thread: ADS805

Greetings People.  I am using two ADS805 devices, each in the configuration shown in figure 7 in the data sheet (Single ended DC coupled input between 0 and +5V).  My sample clock is running at 5MHz.  The problem is the parts are claiming a DC offset.  I shorted both parts' +in pins to ground.  One device is showing 0x10f and the other one is showing 0x118.  This corresponds to 331mV and 343mV.  Has anybody else seen this?

Thanks for looking at this.

Len

  • 0
    Prodigy 40 points
    Sorry folks, I'm an idiot. I was powering +5V from a CMOD_A7 board and I was powering that off a USB connection. To make matters worse, that "+5V" was then being filtered. The result was ~4.4V at the +5V input. When I changed things to bring the ADS805 power up to +5, the offset went away.
  • 0 in reply to Len Epstein
    TI__Mastermind 29220 points

    Hi,

    Thanks for letting us know it was resolved.   I was just going through the datasheet and calculating the typical and max offset in terms of output codes and mV from the % values that are specified in the datasheet, and saw that the offsets you were seeing was indeed excessive.   But I couldn't see a reason why they should be, so I am glad it is resolved.

    Regards,

    Richard P.